1. Field of the Invention
The present invention relates to a technique about a printing apparatus for outputting printed materials. More particularly, the invention relates to a technique for applying to a printing material a control strip for color management and the like of the printed materials to be outputted.
2. Description of the Background Art
In recent years, a printing apparatus equipped with a prepress (or plate-making) mechanism which contains a prepress means for recording an image on a printing plate for use in printing has been known in the art. A general offset printing apparatus, inclusive of such a printing apparatus equipped with the prepress mechanism, comprises an ink fountain mechanism having a plurality of ink keys so that a variable amount of ink supply is set for each of a plurality of ink key regions extending in the feed direction of a printing sheet. With such a printing apparatus, a control strip having patches for color management arranged in corresponding relation to the respective widths of the ink keys is printed in the margin of the printing sheet. It is common practice to adjust the amount of ink supply for each ink key, based on the printed density of the control strip.
A printed sheet with the control strip applied thereto is sampled for every appropriate number of printed sheets by an operator, and is subjected to a printed density measurement by means of a calorimeter and the like provided outside the printing apparatus. Recently, it has been possible to automatically measure the control strip in the printing apparatus by the use of an in-line printed matter measuring device disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-253054. The provision of such an in-line measuring device produces a great effect in being able to automatically control the amount of ink supply and the like at all times without the need for an operator.
When a printing apparatus executes different print jobs in succession, images to be printed in the individual print jobs sometimes differ in dimension in a direction perpendicular to the print direction from each other. In such a case, the control strip is applied by the following methods.
A first method is to always apply a control strip having a maximum length. A second method is to cut the control strip in accordance with the dimension in the direction perpendicular to the print direction of an image to be printed before applying the control strip.
In the first method, control strip image data corresponding to the maximum length of the control strip is previously combined with print image data about an image to be printed. Prepress and printing are carried out based on the combined image data.
However, since the control strip having the maximum length is always applied, this method is disadvantageous in being unable to shorten the time required to execute RIP (Raster-Image-Processing) on the combined image data and the time to subsequently form an image on a printing plate even if the print image data itself is small in size.
The second method is to cut (or trim) the control strip image data corresponding to the maximum length in accordance with the dimension in the direction perpendicular to the print direction of the image to be printed and then to combine the resultant data with the print image data.
The second method does not cause the problem encountered in the first method, but is able to shorten the time for the RIP process and the time for the image formation if the print image data itself is small in size.
In the second method, however, the control strip is mechanically cut in accordance with the dimension in the direction perpendicular to the print direction of the image to be printed. Hence, there is a likelihood that patches indistinguishable in measurement of the printed density are present on opposite ends of the control strip. When the in-line printed matter measuring device for automatically measuring the control strip is provided in the printing apparatus as described above, the control of the amount of ink supply in an ink key corresponding to an end portion of the print image might become unstable due to the indistinguishable patches and ineffective measurement values calculated.